This application is based on Japanese Patent Application Hei 9-130131 filed on May 20, 1997, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to resist composition and a resist pattern forming method, and more particularly to resist composition suitable for exposure of short wavelength light such as excimer laser and a resist pattern forming method.
b) Description of the Related Art
With recent advancements of high integration in semiconductor integrated circuit devices, a sub-half micron rule (minimum line width) is now used for wiring patterns. It is desired to urgently establish micro processing techniques. In order to meet such requirements, short wavelength technologies have been vigorously developed in the field of photolithography in which exposure light is changing from a far ultraviolet range to a deep ultraviolet range. As the wavelength of exposure light becomes short, it is an urgent need to develop resist material which has a low light absorption and a high sensitivity in the short wavelength range and a high resistance to dry etching.
As new exposure technologies of semiconductor manufacture processes, photolithography techniques using krypton fluoride (KrF) excimer laser of 248 nm wavelength have been studied widely. As the resist material having a high sensitivity and a high resolution relative to KrF excimer laser, a resist composition incorporating a concept called a chemically amplified type has been proposed (for example, refer to Proc. Microcircuit Eng., 260 (1982) by J. M. J. Frechet et al, Digest of Technical Papers of 1982 Symposium on VLSI Technology by H. Ito et al, xe2x80x9cPolymers in Electronicsxe2x80x9d by H. Ito et al, ACS Symposium Series 242, compiled by T. Davidson, ACS, 11 (1984), and U.S. Pat. No. 4,491,628).
The fundamental concept of this resist composition is based upon an apparent improvement on a quantum yield and hence an improved sensitivity obtained by catalyst reaction in a resist film.
A chemically amplified type resist composition will be described by taking as an example a resist composition containing t-butoxycarbonyl polyvinylphenol (t-BOCPVP) added with photoacid generator (PAG) having a function of forming acid when light is applied. In the light exposed area of a resist, a t-BOC group is eliminated by a thermal process after the exposure, a so-called post exposure baking (PEB), and isobutene and carbon dioxide are produced. This deprotection reaction progresses catalytically when t-BOC group was eliminated, to produce the polarity change in the exposed area. By selecting a developer suitable for such a large polarity change in the exposed area, a resist pattern can be easily formed.
In order to realize integrated circuit devices of higher integration, photolithography technologies using argon fluoride (ArF) excimer laser having a wavelength (193 nm) shorter than KrF excimer laser have been studied widely. Phenol resin has a high absorption at this wavelength and so it is necessary to develop other base resins.
If a carboxylic acid ester plays a chemically amplifying part at a side chain of a monomer unit of a polymer constituting a chemically amplified type resist, known protective groups suitable for this carboxyl group are only a t-butyl group, 1,1-dimethylbenzyl group, a tetrahydropyranyl group, a 3-oxocyclohexyl group, an isobornyl group and the like. It is highly desired to provide more effective protective groups.
It is an object of the present invention to provide a resist composition suitable for exposure light in a deep ultraviolet range, typically KrF or ArF excimer laser.
It is another object of the present invention to provide a resist pattern forming method which uses a resist composition suitable for exposure light in a deep ultraviolet range, typically KrF or ArF excimer laser.
According to one aspect of the present invention, there is provided a resist composition comprising: a polymer containing a carboxyl group with a protection group at a side chain of a monomer unit, the polymer being insoluble to basic aqueous solution and becoming soluble to basic aqueous solution when the protective group of the carboxyl group is eliminated from the side chain, the protective group of the carboxyl group being represented by: 
where R is a hydrogen atom or a single-bonded hydrocarbon group, n is an integer 1 to 4, and R is attached to a position other than the ester attached the third position.
According to another aspect of the present invention, there is provided a method of forming a resist pattern comprising the steps of: coating a resist material containing the above-described resist composition added with a photoacid generator on a substrate to form a resist film; selectively exposing the resist film with light capable of inducing dissolution of the photoacid generator; and developing the exposed resist film with basic aqueous solution.
As the resist film made of the resist material containing the resist composition added with the photoacid generator is exposed, acid is generated in the exposed area. The acid eliminates the protective group of the carboxyl group. At this time, protonic acid is generated. The reaction of the protonic acid eliminates the protective group of the carboxyl group. Since acid necessary for elimination of the protective group can be regenerated in the above manner, sensitivity can be improved.
This resist material does not contain any aromatic rings and conjugated double bonds having a strong absorption in the deep ultraviolet region, so that high transparency can be obtained in the deep ultraviolet region. It is therefore possible to use this resist material with photolithography using exposure light of a very short wavelength such as ArF excimer laser.
As above, it is possible to provide a resist composition capable of forming a fine positive resist pattern with less swelling at a practical sensitivity.